Addiction may be caused by disordered decision making and reward processing. Thus, understanding the neural mechanisms of reward-guided decision making has the potential to help those addicted to drugs of abuse. One particular brain region, posterior cingulate cortex (CGp), has been implicated in a variety of decision making processes relevant to addiction, including those choices involving risk, time, and social information. Recent studies have suggested that neuronal responses in CGp may encode the subjective value of a chosen option during decisions about risk and time. Thus, a central hypothesis of CGp function is that it is part of a specialized system that integrates information from multiple sources into a single common metric of value. However, one major limitation of these earlier studies is that they have focused on a single decision context (e.g.., risk or delay), but true subjective value representations should be independent of context. Another mystery about CGp function concerns its relationship with the anterior cingulate cortex (ACC), particularly in those decisions involving delays, risk, and social information. A comparison could potentially shed light on the roles of both regions, as well as the mechanisms of reward-based decision making in general, as there are strong reciprocal connections between the two. I am proposing three separate experiments to address these gaps in the literature. I will record responses of single neurons in CGp and ACC during a task involving three different decision contexts relevant to addiction: risk, delay discounting, and social reinforcement. I hypothesize that firing rates of CGp neurons will signal subjective value independent of decision context, and that response modulations of ACC neurons will be greater than those of CGp neurons during decisions involving social reinforcement, whereas CGp neurons will have relatively larger modulations to decisions involving risk. Finally, I will test whether firing patterns observed in CGp play a causal role in decision making by reversibly inactivating this region. Addiction can be framed as a problem of decision making, of failing to make good decisions about risks, rewards, and delaying gratification. Knowing how the brain makes decisions can be of enormous use in trying to understand and solve the complex health problem of addiction to drugs of abuse. I propose to study how a particularly mysterious brain region known as cingulate cortex guides how we process rewards and make decisions, which may advance our progress toward solving the problem of addiction.